Why don’t MegaMix mixtures contain ketones required by the methods?
In methanol solution, ketones can interact with other compounds, resulting in a methoxy addition to the ketone. The presence of halogenated compounds greatly speeds the reaction, limiting shelf-life to less than two months. Because none of eighteen preservatives (including water) was successful at inhibiting the reaction, we do not combine ketones with halogenated compounds in any of our calibration mixtures.
 A comparison of ketone stability in calibration mixes for EPA Method 524.2 Revision 4.0, Christopher Cox, et. al., 1997 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, poster number 467P.